The present invention relates to improved shock and abrasive resistant laminated articles and to their manufacture for use in numerous applications where resistance to abrasion or the combined qualities of impact and wear resistance are required, such as in road scrapers and snow plows by way of example, and in particular for use in modular panels adapted to be assembled together and secured to the floor and walls of chutes, hoppers, bins and the like to provide an area cover or liner in sliding contact with such materials as crushed rock, coal, ore, grain and other abrasive aggregates involved in the mining, foundry, milling, and other material handling industries.
The superior resistance of polyurethane and aluminum oxide ceramics to abrasion has long been recognized. It has been common to utilize such materials in panels for lining surfaces subject to unusual abrasion. A particular form of ceramic known as "weldable tile" has been secured by welding to a steel substrate to provide a panel module. A number of such modules would then be welded or bolted in side-by-side relationship to the floor or wall to be protected. In the alternative, a multitude of approximately four inch square tiles would be laid in juxtaposition with each other to cover a supporting substrate such as a steel plate to which they were secured by an epoxy cement.
Although the abrasion resistance of both the tile and polyurethane is many times that of steel, and the tile is even superior to polyurethane, the ceramic tile available for use as a wear resistant liner is extremely brittle and susceptible to chipping and breakage. Its use has accordingly been limited to situations where the liner is not subject to appreciable shock. Also when the tile cemented to a substrate eventually wears, it is frequently impractical to remove the worn tile. As a result, the entire substrate must be removed and replaced at considerable expense. When the tile is welded to a sheet steel substrate, the heat of the welding frequently stresses the tile and increases its susceptibility to breakage by subsequent impact. The steel substrate thus had to be particularly heavy and thick, as for example on the order of a quarter inch even for light duty panels, in order to provide the necessary rigidity to prevent its flexing and the consequent cracking of the stressed tile.
Attempts have been made to secure abrasive resistant ceramic tile to a cushioning support capable of absorbing shock and reducing tile breakage. Heretofore there has been no satisfactory means for bonding the tile to an elastomeric cushioning support, and in particular to a polyurethane support having the abrasion resistance, elasticity, tensile strength, and tear resistance that render it especially suitable for the cushioning support. Although various polyurethane primers and cements were known, their use for securing tile to polyurethane was complex and costly and required carefully controlled conditions in order to avoid unpredictable and inadequate bonding.
Important objects of the present invention are to provide an economical and readily controlled method for achieving a superior bond between an elastomer, such as a polymerized polyurethane, and smooth surfaces, including sheet steel and abrasion resistant ceramic tile; to provide improved laminated articles of manufacture by the method described herein, which are capable of withstanding severe abrasion; and in particular to provide improved means for bonding brittle abrasive resistant ceramic tile to an elastomeric cushioning support so as to reduce tile breakage and enable the provision of an improved modular panel that may be replacably installed with a plurality of similar panels to provide an abrasive and shock resistant area cover or liner.
Another object is to provide an improved impact and abrasion resistant article of manufacture comprising a ceramic tile positively bonded to a shock absorbing polyurethane base, which in turn if desired is also positively bonded to a hard smooth surfaced support such as sheet steel. Welding operations and the consequent internal stressing of the tile by welding heat are thus avoided and the sheet steel substrate need not provide the rigidity that would otherwise be required. The substrate may accordingly be a light-weight steel sheet to which attachment studs may be welded, or it may be dispensed with entirely in many applications. In any event, the elastomeric support afforded by the polyurethane base materially increases the resistance of the ceramic tile to breakage by impact.
Another important object of the invention is to provide improved means for bonding a polymerized polyurethane layer to a member having a smooth hard surface, wherein the bond comprises a multitude of very short thin fibers partially embedded in the surface of the polyurethane and also in a thin adhesive such as an epoxy resin layer bonded in turn to the smooth surface to complete a laminated article.
Another object is to provide an improved method of manufacturing such an article wherein the smooth surface is provided with a thin coating amounting to approximately two or three thousandths of an inch in thickness of a liquid uncured epoxy resin capable of bonding firmly to the smooth surface when cured thereon. The liquid resin is then dusted with a multitude of the short fibers having a length approximately ten times the thickness of the liquid resin layer, whereby a minor portion of each of the separate fibers is wet by the liquid resin and immersed therein. The remaining major portion of each fiber will of course project from the resin. The resin is then at least partially cured to firmly grip the fibers embedded therein, whereupon any fibers that were not in contact with the wet resin are blown from the cured resin coating to assure that a portion of each fiber remaining is bonded to the resin layer. Thereafter an uncured liquid polyurethane is forced under pressure against the cured resin layer to embed the aforesaid remaining major portion of the fibers within the uncured polyurethane. The latter is then cured with the fibers embedded therein to complete the bond between the polyurethane and the aforesaid smooth hard surface.
Although the cured polyurethane adheres to most smooth surfaces, including the epoxy resin and such synthetics as nylon and rayon from which the aforesaid fibers are preferably formed, the adhesion obtained heretofore was inadequate for articles employed for use and subject to the abuse contemplated herein. It is accordingly a concept of the present invention to effect the bond between the resin and polyurethane by means of fibers having a diameter so small that the tensile strength of any one fiber is on the order of magnitude of the adhesive force between the polyurethane and that fiber. Inasmuch as the adhesion between the fiber and the polyurethane is proportional to the surface area or circumference of the fiber, when a fiber is split longitudinally into a multitude of smaller diameter fibers, the total periphery of the resulting fibers and the consequent adhesion to the polyurethane may be increased greatly without effecting the total cross-sectional area or tensile strength of the fibers.
Other objects are accordingly to utilize fibers such as nylon or rayon sufficiently small in diameter that as many as approximately 300,000 fibers per square inch may be embedded in the epoxy resin, and to provide electrostatic means for orienting the fibers in the resin to reduce their matting and to assure that the major portions of the lengths of the fibers extend outward from the resin layer to enhance their bonding to the polyurethane.
Another and more specific object is to preheat the member having the smooth hard surface prior to applying the liquid resin, thereby to reduce the viscosity of the liquid resin when it is thereafter applied and to allow any excess resin to drip or drain from the member.
Another object is to provide a method substantially as described above for fabricating an abrasion and shock resistant composite panel comprising an elastomeric cushioning support of polyurethane having a plurality of ceramic tiles bonded thereon and spaced from a sheet steel backing also bonded to the polyurethane. The sheet steel backing and the tiles with the cured epoxy resin layer and adhering fibers are supported in an injection mold cavity. The tiles are arranged in side-by-side and slightly spaced relationship with their fiber covered surfaces confronting and spaced from a similar fiber covered surface of the sheet steel backing to provide a space in the mold cavity to be filled with polyurethane. Uncured polyurethane in a liquid state is then injected by the aforesaid pressure into the latter space to fill the same and force the polyurethane into the spaces between the tiles and against the fiber covered surfaces to embed the extending portions of the fibers into the adjacent polyurethane. By virtue of the mechanical interlock effected by the multitude of thin fibers, a superior bond between the polyurethane and both the tile and steel layers is achieved and an otherwise conventional injection molding technique is rendered feasible in the formation of the laminated article.
Another object is to provide a laminated panel comprising a number of abrasion resistant cylindrical ceramic tiles preferably of circular or hexagonal cross-sectional and of comparatively small diameter approximately equal to an inch plus or minus a half inch, arranged side-by-side with their principal axes parallel to provide a ceramic wear resistant surface that it also very shock or impact resistant. The surface of each tile is bonded as described herein to the elastomeric polyurethane cushioning support, which in turn may be similarly bonded to a sheet steel backing.
The separate tiles are preferably spaced by and bonded to intervening extensions of the polyurethane support and are independently cushioned by the polyurethane such that the major area of the wear resistant panel is shielded from severe localized shocks. A blow or sudden force to any one tile, for example, directed against its exposed end at the wear resistant surface will be transmitted through that tile and absorbed by the polyurethane support without significantly transmitting the force of the blow to the radially adjacent tiles.
Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.